ARM: dts: imx6qdl-apalis/-colibri: disable read-only switch

Use the disable-wp to indicate that Apalis and Colibri iMX6 do not
make use of the native write-protect signal available on the i.MX 6
SoCs. This prevents warnings:
  mmc0: host does not support reading read-only switch, assuming write-enable

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>